The first commercial solar water heater called the "Climax" was patented in 1891 by Clarence Kemp.  It is considered a batch or I.C.S. system.  In 1909, the first modern style solar water heating system called  the "Day and Night" was patented by William J. Bailey.  It used separate tanks and collectors in a thermo siphon system.  These early systems competed with wood and coal stoves.  Later models competed against natural gas water heaters.  In the early 1980's there was a renewed interest in solar thermal as fossil fuel prices rose due to the Arab oil embargo.  This trend was short lived as Natural Gas was deregulated in the mid 1980's.  Recent increases in the price of natural gas has again helped spur growth in solar thermal.  Many incremental advances over the years have improved solar thermal collector efficiency and durability. 

Germany has become the world leader in solar energy largely due to a tense relationship with their primary source of natural gas in Russia.  Germany developed a self reliant psychology towards energy that made solar energy more attractive.  The U.S. currently has a more discretionary attitude about renewable energy.